Editing Reptile (section)

==Classification==
{{see also|List of reptiles}}

===Research history===
{{See also|Skull roof}}
[[File:Reptile003d.jpg|thumb|right|Reptiles, from ''Nouveau Larousse Illustré'', 1897–1904, notice the inclusion of [[amphibian]]s (below the crocodiles)]]

In the 13th century, the category of ''reptile'' was recognized in Europe as consisting of a miscellany of egg-laying creatures, including "snakes, various fantastic monsters, lizards, assorted amphibians, and worms", as recorded by [[Vincent of Beauvais|Beauvais]] in his ''Mirror of Nature''.<ref>{{cite book | last = Franklin-Brown | first = Mary | year = 2012 | title = Reading the World : Encyclopedic writing in the scholastic age | publisher = The University of Chicago Press | location = Chicago, IL / London, UK | isbn = 9780226260709 |pages=223, 377}}</ref>
In the 18th century, the reptiles were, from the outset of classification, grouped with the [[amphibian]]s. [[Carl Linnaeus|Linnaeus]], working from species-poor [[Sweden]], where the [[common adder]] and [[grass snake]] are often found hunting in water, included all reptiles and amphibians in [[class (biology)|class]] [[Amphibia in the 10th edition of Systema Naturae|{{nobr|"III – Amphibia"}}]] in his ''[[Systema Naturæ]]''.<ref name=Linn1758>{{cite book |last=Linnaeus |first=Carolus |author-link=Carl Linnaeus |year=1758 |title=Systema naturae per regna tria naturae: Secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis |language=la |trans-title=System of Nature through the Three Natural Kingdoms, According to classes, orders, genera, species, with characters, differences, synonyms, places |edition=10th |publisher=Holmiae (Laurentii Salvii) |url=https://www.biodiversitylibrary.org/bibliography/542 |access-date=September 22, 2008}}</ref>
The terms ''reptile'' and ''amphibian'' were largely interchangeable, ''reptile'' (from Latin ''repere'', 'to creep') being preferred by the French.<ref>{{cite encyclopedia |title=Amphibia |encyclopedia=Encyclopædia Britannica |edition=9th |year=1878 |url=http://aleph0.clarku.edu/huxley/UnColl/EnBrit/Amphibia.html}}</ref> [[Josephus Nicolaus Laurenti|J.N. Laurenti]] was the first to formally use the term ''Reptilia'' for an expanded selection of reptiles and amphibians basically similar to that of Linnaeus.<ref>{{cite book |author=Laurenti, J.N. |author-link=Josephus Nicolaus Laurenti |year=1768 |title=Specimen medicum, exhibens synopsin reptilium emendatam cum experimentis circa venena |language=la |trans-title=Medical Specimen: Presenting an improved synopsis of reptiles with experiments on poisons |url=http://gdz.sub.uni-goettingen.de/no_cache/dms/load/img/?IDDOC=281657 |format=facsimile |archive-url=https://web.archive.org/web/20150904013401/http://gdz.sub.uni-goettingen.de/no_cache/dms/load/img/?IDDOC=281657 |archive-date=2015-09-04 }} — shows the mixed composition of ''Reptilia''.</ref> Today, the two groups are still commonly treated under the single heading [[herpetology]].

[[File:MosasaurDiscovery.jpg|thumb|left|"Antediluvian monster", a ''[[Mosasaurus]]'' discovered in a [[Maastricht]] limestone quarry, 1770 (contemporary engraving)]]

It was not until the beginning of the 19th century that it became clear that reptiles and amphibians are, in fact, quite different animals, and [[Pierre André Latreille|P.A. Latreille]] erected the class ''Batracia'' (1825) for the latter, dividing the [[tetrapod]]s into the four familiar classes of reptiles, amphibians, birds, and mammals.<ref>{{cite book |author=Latreielle, P.A. |author-link=Pierre André Latreille |year=1804 |title=Nouveau Dictionnaire à Histoire Naturelle |language=fr |trans-title=New Dictionary of Natural History |page=xxiv}} cited in {{cite book |author=Latreille, P.A. |year=1825 |title=Familles naturelles du règne animal, exposés succinctement et dans un ordre analytique |language=fr |trans-title=Natural families of the animal kingdom, succinctly presented in analytical order}}</ref> The British anatomist [[Thomas Henry Huxley|T.H. Huxley]] made Latreille's definition popular and, together with [[Richard Owen]], expanded Reptilia to include the various fossil "[[antediluvian]] monsters", including [[dinosaur]]s and the mammal-like ([[synapsid]]) ''[[Dicynodon]]'' he helped describe. This was not the only possible classification scheme: In the Hunterian lectures delivered at the [[Royal College of Surgeons of England|Royal College of Surgeons]] in 1863, Huxley grouped the vertebrates into [[mammal]]s, sauroids, and ichthyoids (the latter containing the fishes and amphibians). He subsequently proposed the names of [[Sauropsida]] and [[Ichthyopsida]] for the latter two groups.<ref>{{cite periodical |author=Huxley, T.H. |author-link=Thomas Henry Huxley |year=1863 |title=The structure and classification of the Mammalia |series=Hunterian lectures |periodical=Medical Times and Gazette |url=http://aleph0.clarku.edu/huxley/UnColl/Gazettes/Mamma.html}}</ref> In 1866, [[Ernst Haeckel|Haeckel]] demonstrated that vertebrates could be divided based on their reproductive strategies, and that reptiles, birds, and mammals were united by the [[amniotic egg]].

The terms ''Sauropsida'' ("lizard faces") and ''[[synapsid|Theropsida]]'' ("beast faces") were used again in 1916 by [[Edwin Stephen Goodrich|E.S. Goodrich]] to distinguish between lizards, birds, and their relatives on the one hand (Sauropsida) and [[mammal]]s and their extinct relatives (Theropsida) on the other. Goodrich supported this division by the nature of the hearts and blood vessels in each group, and other features, such as the structure of the forebrain. According to Goodrich, both lineages evolved from an earlier stem group, Protosauria ("first lizards") in which he included some animals today considered [[Reptiliomorpha|reptile-like amphibians]], as well as early reptiles.<ref name=goodrich1916>{{cite journal |last=Goodrich |first=E.S. |title=On the classification of the Reptilia |journal=Proceedings of the Royal Society of London B |volume=89 |pages=261–276 |year=1916 |doi=10.1098/rspb.1916.0012 |doi-access=free |issue=615|bibcode=1916RSPSB..89..261G }}</ref>

In 1956, [[D. M. S. Watson|D.M.S. Watson]] observed that the first two groups diverged very early in reptilian history, so he divided Goodrich's Protosauria between them. He also reinterpreted Sauropsida and Theropsida to exclude birds and mammals, respectively. Thus his Sauropsida included [[Procolophonia]], [[Eosuchia]], [[Millerettid|Millerosauria]], [[Turtle|Chelonia]] (turtles), [[Squamata]] (lizards and snakes), [[Sphenodontia|Rhynchocephalia]], [[Crocodilia]], "[[Thecodontia|thecodonts]]" ([[paraphyly|paraphyletic]] [[basal (phylogenetics)|basal]] [[Archosaur]]ia), non-[[wikt:avian|avian]] [[dinosaur]]s, [[pterosaur]]s, [[ichthyosaur]]s, and [[sauropterygia]]ns.<ref name=watson1956>{{cite journal |last=Watson |first=D.M.S. |year=1957 |title=On millerosaurus and the early history of the sauropsid reptiles |journal=Philosophical Transactions of the Royal Society of London B |volume=240 |issue=673 |pages=325–400 |doi=10.1098/rstb.1957.0003 |doi-access=free |bibcode=1957RSPTB.240..325W}}</ref>

In the late 19th century, a number of definitions of Reptilia were offered. The biological traits listed by [[Richard Lydekker|Lydekker]] in 1896, for example, include a single [[occipital condyle]], a jaw joint formed by the [[Quadrate bone|quadrate]] and [[articular]] bones, and certain characteristics of the [[Vertebral column|vertebrae]].<ref>{{cite book |last=Lydekker |first=Richard |year=1896 |series=The Royal Natural History |title=Reptiles and Fishes |pages=[https://archive.org/details/in.ernet.dli.2015.110219/page/n26 2]–3 |publisher=Frederick Warne & Son |location=London, UK |url=https://archive.org/details/in.ernet.dli.2015.110219 |access-date=March 25, 2016}}</ref> The animals singled out by these formulations, the [[amniote]]s other than the mammals and the birds, are still those considered reptiles today.<ref name="tudge"/>

[[File:Captorhinus aguti p.jpg|thumb|right|The first reptiles had an [[anapsid]] type of [[skull roof]], as seen in the [[Permian]] genus ''[[Captorhinus]]'']]

The synapsid/sauropsid division supplemented another approach, one that split the reptiles into four subclasses based on the number and position of [[temporal fenestra]]e, openings in the sides of the skull behind the eyes. This classification was initiated by [[Henry Fairfield Osborn]] and elaborated and made popular by [[Alfred Romer|Romer]]'s classic ''[[Vertebrate Paleontology (Romer)|Vertebrate Paleontology]]''.<ref>{{cite journal | last1=Osborn | first1=H.F. | author-link=Henry Fairfield Osborn | year=1903 | title=The reptilian subclasses ''Diapsida'' and ''Synapsida'' and [the] early history of ''Diaptosauria'' | journal=Memoirs of the American Museum of Natural History | volume=1 | pages=451–507 }}</ref><ref name=romer1933>{{cite book |last=Romer |first=A.S. |author-link=Alfred Romer |orig-year=1933 |year=1966 |title=Vertebrate Paleontology |edition=3rd |publisher=University of Chicago Press |place=Chicago, IL}}</ref> Those four subclasses were:
* [[Anapsid]]a – no fenestrae – [[Captorhinida|cotylosaurs]] and [[turtle|chelonia]] ([[turtle]]s and relatives){{efn|
This taxonomy does not reflect modern molecular evidence, which places turtles within [[Diapsida]].
}}
* [[Synapsida]] – one low fenestra – [[pelycosaur]]s and [[therapsid]]s (the '[[mammal-like reptiles]]')
* [[Euryapsida]]&nbsp;– one high fenestra (above the postorbital and squamosal)&nbsp;– [[protorosaur]]s (small, early lizard-like reptiles) and the marine [[sauropterygia]]ns and [[ichthyosaurs]], the latter called [[Parapsida]] in Osborn's work.
* [[Diapsid]]a – two fenestrae – most reptiles, including [[lizard]]s, [[snake]]s, [[crocodilian]]s, [[dinosaur]]s and [[pterosaur]]s.

[[File:Varanodon1DB.jpg|thumb|right|Phylogenetic classifications group the traditional "mammal-like reptiles", like this ''[[Varanodon]]'', with other synapsids, not with extant reptiles]]
The composition of Euryapsida was uncertain. [[Ichthyosaurs]] were, at times, considered to have arisen independently of the other euryapsids, and given the older name Parapsida. Parapsida was later discarded as a group for the most part (ichthyosaurs being classified as ''[[incertae sedis]]'' or with Euryapsida). However, four (or three if Euryapsida is merged into Diapsida) subclasses remained more or less universal for non-specialist work throughout the 20th&nbsp;century. It has largely been abandoned by recent researchers: In particular, the anapsid condition has been found to occur so variably among unrelated groups that it is not now considered a useful distinction.<ref>{{cite journal |last1=Tsuji |first1=L.A. |last2=Müller |first2=J. |year=2009 |title=Assembling the History of the Parareptilia: Phylogeny, diversification, and a new definition of the clade |journal=Fossil Record |volume=12 |issue=1 |pages=71–81 |doi=10.1002/mmng.200800011 |bibcode=2009FossR..12...71T |doi-access=free}}</ref>

===Phylogenetics and modern definition===
By the early 21st century, vertebrate paleontologists were beginning to adopt [[phylogenetic]] taxonomy, in which all groups are defined in such a way as to be [[clade|monophyletic]]; that is, groups which include all descendants of a particular ancestor. The reptiles as historically defined are [[paraphyly|paraphyletic]], since they exclude both birds and mammals. These respectively evolved from dinosaurs and from early therapsids, both of which were traditionally called "reptiles".<ref name=Brysse2008>{{cite journal |last=Brysse |first=K. |year=2008 |title=From weird wonders to stem lineages: The second reclassification of the Burgess Shale fauna |journal=Studies in History and Philosophy of Science Part C: Biological and Biomedical Sciences |volume=39 |issue=3 |pages=298–313 |doi=10.1016/j.shpsc.2008.06.004 |pmid=18761282 }}</ref> Birds are more closely related to [[crocodilian]]s than the latter are to the rest of extant reptiles. [[Colin Tudge]] wrote:

<blockquote>Mammals are a [[clade]], and therefore the [[Phylogenetic nomenclature|cladists]] are happy to acknowledge the traditional taxon [[Mammal]]ia; and birds, too, are a clade, universally ascribed to the formal taxon [[bird|Aves]]. Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class Reptilia is not a clade. It is just a section of the clade [[Amniota]]: The section that is left after the Mammalia and Aves have been hived off. It cannot be defined by [[synapomorphy|synapomorphies]], as is the proper way. Instead, it is defined by a combination of the features it has and the features it lacks: reptiles are the amniotes that lack fur or feathers. At best, the cladists suggest, we could say that the traditional Reptilia are 'non-avian, non-mammalian amniotes'.<ref name=tudge>{{RefTudgeVariety}}</ref></blockquote>

Despite the early proposals for replacing the paraphyletic Reptilia with a monophyletic [[Sauropsida]], which includes birds, that term was never adopted widely or, when it was, was not applied consistently.<ref name=modestoanderson2004>{{cite journal | last1=Modesto | first1=S.P. | last2=Anderson | first2=J.S. | year=2004 | title=The phylogenetic definition of Reptilia | journal=Systematic Biology | pmid=15545258 | volume=53 | issue=5 | pages=815–821 | doi=10.1080/10635150490503026 |doi-access=free}}</ref>

[[File:Bearded Dragon Skeleton.jpg|thumb|Bearded dragon ([[pogona]]) skeleton on display at the [[Museum of Osteology]]]]
When Sauropsida was used, it often had the same content or even the same definition as Reptilia. In 1988, [[Jacques Gauthier]] proposed a [[cladistics|cladistic]] definition of Reptilia as a monophyletic node-based [[crown group]] containing turtles, lizards and snakes, crocodilians, and birds, their common ancestor and all its descendants. While Gauthier's definition was close to the modern consensus, nonetheless, it became considered inadequate because the actual relationship of turtles to other reptiles was not yet well understood at this time.<ref name=modestoanderson2004/> Major revisions since have included the reassignment of synapsids as non-reptiles, and classification of turtles as diapsids.<ref name=modestoanderson2004/> Gauthier 1994 and Laurin and Reisz 1995's definition of Sauropsida defined the scope of the group as distinct and broader than that of Reptilia, encompassing [[Mesosauridae]] as well as Reptilia ''sensu stricto''.<ref name="Gauthier-1994-Prothero-Schoch" /><ref name="Laurin 95" />

A variety of other definitions were proposed by other scientists in the years following Gauthier's paper. The first such new definition, which attempted to adhere to the standards of the [[PhyloCode]], was published by Modesto and Anderson in 2004.<ref name=modestoanderson2004/> Modesto and Anderson reviewed the many previous definitions and proposed a modified definition, which they intended to retain most traditional content of the group while keeping it stable and monophyletic. They defined Reptilia as all amniotes closer to ''[[Lacerta agilis]]'' and ''[[Crocodylus niloticus]]'' than to ''[[Homo sapiens]]''. This stem-based definition is equivalent to the more common definition of Sauropsida, which Modesto and Anderson synonymized with Reptilia, since the latter is better known and more frequently used. Unlike most previous definitions of Reptilia, however, Modesto and Anderson's definition includes birds, as they are within the clade that includes both lizards and crocodiles.<ref name=modestoanderson2004/>

===Taxonomy===
{{See also|List of reptiles|List of snakes}}
General classification of extinct and living reptiles, focusing on major groups.<ref name=benton2005>{{cite book |last=Benton |first=Michael J. |author-link=Michael J. Benton |year=2005 |title=Vertebrate Palaeontology |edition=3rd |publisher=Blackwell Science |location=Oxford, UK |isbn=978-0-632-05637-8 |url=http://palaeo.gly.bris.ac.uk/benton/vertclass.html |access-date=2015-02-15 |archive-date=2008-10-19 |archive-url=https://web.archive.org/web/20081019121413/http://palaeo.gly.bris.ac.uk/benton/vertclass.html |url-status=dead }}</ref><ref name=benton2014>{{cite book |last=Benton |first=Michael J. |author-link=Michael J. Benton |year=2014 |title=Vertebrate Palaeontology |edition=4th |publisher=Blackwell Science |location=Oxford, UK |isbn=978-0-632-05637-8}}</ref><!-- Note to editors: the nested infraclasses are as presented in Benton's 4th edition. Infraclass Diapsida contains Infraclass Neodiapsida, which contains infraclasses Archosauromorpha and Lepidosauromorpha, with the latter containing Infraclass Ichthyosauria within an unnamed Infrasubclass -->
* '''Reptilia'''/'''[[Sauropsida]]'''
**{{extinct}}'''[[Parareptilia]]'''
** '''[[Eureptilia]]'''
***{{extinct}}[[Captorhinidae]]
***'''[[Diapsid]]a''' <!-- note that the multiple nested infraclasses is part of the classification in Benton's 4th edition -->
****{{extinct}}[[Araeoscelidia]]
****'''[[Neodiapsida]]'''
*****{{extinct}}[[Drepanosauromorpha]] (placement uncertain)
*****{{extinct}}[[Younginiformes]] ([[paraphyletic]])
*****{{extinct}}[[Ichthyosauromorpha]] (placement uncertain)
*****{{extinct}}[[Thalattosauria]] (placement uncertain)
*****'''[[Sauria]]'''
******'''[[Lepidosauromorpha]]'''
*******[[Lepidosauriformes]]
********[[Rhynchocephalia]] (tuatara)
********[[Squamata]] (lizards and snakes)
******{{extinct}}[[Choristodera]] (placement uncertain)
******{{extinct}}[[Sauropterygia]] (placement uncertain)
******'''[[Pantestudines]]''' (turtles and kin, placement uncertain)
******'''[[Archosauromorpha]]'''
*******{{extinct}}[[Protorosauria]] (paraphyletic)
*******{{extinct}}[[Rhynchosauria]]
*******{{extinct}}[[Allokotosauria]]
*******[[Archosauriformes]]
********{{extinct}}[[Phytosaur]]ia
********'''[[Archosauria]]'''
*********[[Pseudosuchia]]
**********[[Crocodilia]] (crocodilians)
*********[[Avemetatarsalia]]/[[Ornithodira]]
**********{{extinct}}[[Pterosaur]]ia
**********[[Dinosaur]]ia
***********{{extinct}}[[Ornithischia]]
***********[[Saurischia]] (including birds ('''[[Bird|Aves]]'''))

===Phylogeny===
The [[cladistics#Cladograms|cladogram]] presented here illustrates the "family tree" of reptiles, and follows a simplified version of the relationships found by M.S. Lee, in 2013.<ref name=scaffold2013>{{cite journal | last1=Lee | first1=M.S.Y. | year=2013 | title=Turtle origins: Insights from phylogenetic retrofitting and molecular scaffolds | journal=Journal of Evolutionary Biology | volume=26 | issue=12 | pages=2729–2738 | doi=10.1111/jeb.12268 |doi-access=free | pmid=24256520}}</ref> All [[Molecular phylogenetics|genetic]] studies have supported the hypothesis that turtles are diapsids; some have placed turtles within Archosauromorpha,<ref name=scaffold2013/><ref name="Mannen">{{cite journal |author1=Mannena, Hideyuki |author2=Li, Steven S.-L. |year=1999 |title=Molecular evidence for a clade of turtles |journal=[[Molecular Phylogenetics and Evolution]] |volume=13 |issue=1 |pages=144–148 |doi=10.1006/mpev.1999.0640 |pmid=10508547|bibcode=1999MolPE..13..144M }}</ref><ref name=Zardoya/><ref name=Iwabe/><ref name=Roos/><ref name=Katsu/> though a few have recovered turtles as Lepidosauromorpha instead.<ref>{{cite journal |author1=Lyson, Tyler R. |author2=Sperling, Erik A. |author3=Heimberg, Alysha M. |author4=Gauthier, Jacques A. |author5=King, Benjamin L. |author6=Peterson, Kevin J. |year=2012 |title=MicroRNAs support a turtle + lizard clade |journal=[[Biology Letters]] |volume=8 |issue=1 |pages=104–107 |doi=10.1098/rsbl.2011.0477 |doi-access=free |pmid=21775315 |pmc=3259949 |bibcode=2012BiLet...8..104L }}</ref> The cladogram below used a combination of genetic (molecular) and fossil (morphological) data to obtain its results.<ref name=scaffold2013/>

{{clade| style=font-size:80%;line-height:80%
|label1=[[Amniote|Amniota]]
|1={{clade
   |1=[[Synapsida]] ([[mammal]]s and their extinct relatives) [[File:Rattus norvegicus (white background).png|50px]]
   |label2='''[[Sauropsida|Sauropsida / Reptilia]]''' |sublabel2=(total group)
   |2={{clade
         |label1={{extinct}}[[Parareptilia]]
         |1={{clade
               |1={{extinct}}[[Millerettid]]ae [[File:Milleretta BW flipped.jpg|50px]]
               |label2=<span style="color:white;">unnamed</span>
               |2={{clade
                  |1={{extinct}}''[[Eunotosaurus]]''
                  |label2={{extinct}}[[Ankyramorpha]]
                  |2={{clade
                  |1={{extinct}}[[Lanthanosuchidae]] [[File:Lanthanosuchus NT flipped.jpg|50px]]
                  |label2={{extinct}}[[Procolophonia]]
                    |2={{clade
                        |1={{extinct}}[[Pareiasauromorpha]] [[File:Scutosaurus BW flipped.jpg|50px]]
                        |2={{extinct}}[[Procolophonoidea]] [[File:Sclerosaurus1DB.jpg|50px]]
                        }}
                     }}
                 }}
             }}
      |label2=[[Eureptilia]]
      |2={{clade
         |1={{extinct}}[[Captorhinidae]] [[File:Labidosaurus flipped.jpg|50px]]
         |label2=[[Romeriida]]
         |2={{clade
            |1={{extinct}}''[[Paleothyris]]''
            |label2=[[Diapsid]]a
            |2={{clade
               |1={{extinct}}[[Araeoscelidia]] [[File:Spinoaequalis schultzei reconstruction.jpg|50px]]
               |label2=[[Neodiapsida]]
               |2={{clade
               |1={{extinct}}''[[Claudiosaurus]]''[[File:Claudiosaurus white background.jpg|50px]]
               |2={{clade
                  |1={{extinct}}[[Younginiformes]] [[File:Hovasaurus BW flipped.jpg|50px]]
                  |label2='''Crown Reptilia'''/ |sublabel2=[[Sauria]]
                  |2={{clade
                     |label1=[[Pan-Lepidosauria]]/ |sublabel1=[[Lepidosauromorpha]]
                     |1={{clade
                         |1={{extinct}}[[Kuehneosauridae]] [[File:Icarosaurus white background.jpg|50px]]
                         |label2=[[Lepidosauria]]
                         |2={{clade
                            |1=[[Rhynchocephalia]] ([[tuatara]] and their extinct relatives) [[File:Hatteria white background.jpg|50px]]
                            |2=[[Squamata]] ([[lizard]]s and [[snake]]s) [[File:British reptiles, amphibians, and fresh-water fishes (1920) (Lacerta agilis).jpg|50px]] [[File:Python natalensis Smith 1840 white background.jpg|50px]] }} }}
                     |label2=[[Archelosauria]]/ |sublabel2=[[Archosauromorpha]] ''[[sensu lato|s. l.]]''
                     |2={{clade
                        |label1=[[Pan-Testudines]]/ |sublabel2=[[Pantestudines]]
                        |1={{clade
                          |1={{extinct}}[[Eosauropterygia]] [[File:Dolichorhynchops BW flipped.jpg|50px]]
                          |2={{clade
                            |1={{extinct}}[[Placodontia]] [[File:Psephoderma BW flipped.jpg|50px]]
                            |2={{clade
                              |1={{extinct}}''[[Sinosaurosphargis]]''
                              |2={{clade
                                |1={{extinct}}''[[Odontochelys]]''
                                |label2=[[Testudinata]]
                                |2={{clade
                                  |1={{extinct}}''[[Proganochelys]]''
                                  |2=[[Testudines]] ([[turtle]]s) [[File:Erpétologie générale, ou, Histoire naturelle complète des reptiles (Centrochelys sulcata).jpg|50px]]
                                   }}
                                 }}
                               }}
                             }}
                           }}
                        |label2=[[Pan-Archosauria]]
                        |2={{clade
                           |1={{extinct}}[[Choristodera]] <span style="{{MirrorH}}">[[File:Hyphalosaurus mmartyniuk wiki.png|60px]]</span>
                           |label2=[[Archosauromorpha]] ''[[sensu stricto|s. s.]]''
                           |2={{clade
                              |1={{extinct}}[[Prolacertiformes]] [[File:Prolacerta broomi.jpg|50px]]
                              |2={{clade
                                   |2=[[Archosauriformes]] ([[Crocodilia|crocodiles]], [[bird]]s, dinosaurs and extinct relatives) <span style="{{MirrorH}}">[[File:Deinosuchus riograndensis.png|50px]]</span> [[File:Meyers grosses Konversations-Lexikon - ein Nachschlagewerk des allgemeinen Wissens (1908) (Antwerpener Breiftaube).jpg|30 px]]
                                   |1={{clade
                                      |1={{extinct}}[[Rhynchosauria]] [[File:Hyperodapedon BW2 white background.jpg|50px]]
                                      |2={{extinct}}''[[Trilophosaurus]]''[[File:Trilophosaurus buettneri (flipped).jpg|50px]]
                                      }}
                                  }}
                              }}
                           }}
                         }}
                       }}
                     }}
                  }}
               }}
            }}
         }}
      }}
   }}
}}

===The position of turtles===
The placement of turtles has historically been highly variable. Classically, turtles were considered to be related to the primitive anapsid reptiles.<ref name="Romer, A 1977"/> Molecular work has usually placed turtles within the diapsids. As of 2013, three turtle genomes have been sequenced.<ref name=Gilbert2013>{{cite journal | last1=Gilbert | first1=S.F. | last2=Corfe | first2=I. | date=May 2013 | title=Turtle origins: picking up speed | journal=Dev. Cell | volume=25 | issue=4 | pages=326–328 | doi=10.1016/j.devcel.2013.05.011 |doi-access=free | pmid=23725759 | url=http://www.cell.com/developmental-cell/pdf/S1534-5807(13)00285-2.pdf}}</ref>{{update needed|date=July 2024}} The results place turtles as a [[sister clade]] to the [[archosaur]]s, the group that includes crocodiles, non-avian dinosaurs, and birds.<ref>{{cite journal |first1=Ylenia |last1=Chiari |first2=Vincent |last2=Cahais |first3=Nicolas |last3=Galtier |first4=Frédéric |last4=Delsuc |year=2012 |title=Phylogenomic analyses support the position of turtles as the sister group of birds and crocodiles (Archosauria) |journal=BMC Biology |volume=10 |issue=65 |pages=65 |doi=10.1186/1741-7007-10-65 |pmid = 22839781|pmc=3473239 |doi-access=free}}</ref> However, in their comparative analysis of the timing of [[organogenesis]], Werneburg and Sánchez-Villagra (2009) found support for the hypothesis that turtles belong to a separate clade within [[Sauropsida]], outside the [[sauria]]n clade altogether.<ref name="Werneburg and Sánchez-Villagra 2009">{{cite journal |last1=Werneburg |first1=Ingmar |last2=Sánchez-Villagra |first2=Marcelo R. |date=23 April 2009 |title=Timing of organogenesis support[s] basal position of turtles in the amniote tree of life |journal=BMC Evolutionary Biology |volume=9 |issue=1 |page=82 |id=article&nbsp;82 |doi=10.1186/1471-2148-9-82 |pmid=19389226 |pmc=2679012 |bibcode=2009BMCEE...9...82W |issn=2730-7182 |doi-access=free }}</ref>